THE 



AMERICANJOURNALOFSCIENCE 



[FOURTH SERIES.] 



Art. XII. — The Effect of a Magnetic Field on Ionization 

 Currents; by William Duane. 



The effects produced by a magnetic field on the passage 

 of electricity through gases in the arc and spark discharges 

 and in vacuum tubes have been studied in a great many ways, 

 and many important conclusions have been drawn from the 

 experiments. In particular it has been found possible to 

 determine the ratios of the charge e to the mass m of the 

 particles that carry the positive and negative electricity in 

 vacuum tubes. Further, Marx* has observed a transverse 

 electromotive force (analagous to the Hall effect in metals) due 

 to the action of a magnetic field on an electric current flowing 

 through a flame. 



About two years ago the writer undertook to investigate the 

 effect (if any exists) produced by a magnetic field on ionization 

 currents, in which the ionization is due to X-rays and radium 

 rays. It was hoped that accurate measurements could be made 

 from which the ratios e/m for the positive and negative ions 

 could be calculated, and that evidence could be gathered either 

 for or against the supposition that positive electrons exist, 

 which are common to all gases. Some results of preliminary 

 experiments were communicated to the French Academy of 

 Sciencesf in July, 1911, and the object of this paper is to give 

 a description of these experiments. 



The general principles underlying the methods of investiga- 

 tion may be stated as follows : A narrow and intense beam of 

 a- and /8-rays from radium emanation passes parallel to and 

 midway between two parallel metal plates. An electric battery 



* Ann. der Phys., ii, 798, 1900. 



\ Comptes rendus, clii, 1336-339, July, 1911. 



Am. Jour. Sci.— Fourth Series, Vol. XXXV, No. 206.— February, 1913. 

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